question

@Mm2306 If I have matching 2x 100w panels wired the same, is that the same as having the panels wired as series parallel?

Yes you can parallel another 2 of the same panels.

First though you have to work out if the existing panels have been wired to the mppt as 2 series, or 2 parallel.

Have a look at the sticker on the panel for the Vmp voltage. Check what the mppt reports as the "solar voltage". If those 2 figures approximately match, wire your 2 additional panels as parallel.

If the mppt "solar voltage" is about double the panel Vmp, wire the 2 panels in series.

You might have some losses if the arrays point in different directions.

We don't have enough information.

Are the existing pànels wired in series or parallel? If series and the outside plug is connected as you say, two more panels in series will give you the 2s2p configuration.

Couple of things to check.

Assuming same make model of panels from your identical comments, not just power matches.

Voc for each panel. With this make sure that the series combination of 2xVoc is well below 100V and cannot exceed it at your lowest local temperature.

Orientation /angle to sun should be the same for all panels

Make sure suitable cable size used..

Do not connect/disconnect without covering the extra panels first. Any connect/disconnect under load will cause arcing in the connectors and damage them.

Thank you for your inputs- here's a little more detailed info:

I have 2 gopower brand 100w panels wired in series to my mppt. Specs are not easily found and I am not the one who bought them, but I think I found correct numbers online. Specs: VOC 21.0V, Vmp 17.5, Imp 5.68, Inc 6.28. Typical readings on my solar output are 130w output (29-31v at 4.2-4.5a). I have seen as high as 180w output but not typical.

So the rest is a 2 part question. I want to add permanent panels similar in specs to roof (gopower panels are $5xx per panel, I'm not spending that) and have landed on Renogy 100w. Specs on that are: VOC 22.5, Vmp 18.9, Imp 5.29, and Isc 5.75. I will wire 2 of these panels in series and then connect them in parallel to my existing two. So these feed into the input on my MPPT. (First question, are these panels compatible enough with each other? I'm ok with not being maximum efficiency for the sake of saving $700)

2nd question. The exterior panel is a Zamp plug that the previous owner wired into the same input slot of the MPPT of the main panels. Is it OK to wire another 2 similar panel in series as accessory panels to plug into the samp plug that feed into the same input? Is it essentially the same as adding another parallel panel at the same junction as the other 2 series?

Sorry for the lengthy description, trying to be as specific as possible

@Mm2306 the Go Power panel has 32 cells and the Renogy panel has 36 cells.

You cannot mix those 2 types of panels on 1 mppt. The voltage difference is to much.

If you dont want to replace the Go Power panels, find some 32 cell panels that will have higher chance of the Voc & Vmp being similar.

Dunno what a Zamp connector is. Use either Anderson or MC4 connectors. Take note what @kevgermany has mentioned about connecting / disconnecting panels under load. Zap!!